The invention relates to optical networks and their components. More specifically, the invention relates to optical cross connects for dense wavelength division multiplexing, or DWDM networks.
Fibre optic networks allow very large amounts of information to be transmitted accurately over long and short distances. These networks transmit a plurality of optical signals with differing wavelengths into the same fibre to increase the overall bandwidth of the network. Referring to FIG. 1, an optical network is shown wherein a plurality of optical signals with different wavelengths, xcex1 to xcexn, is transmitted from a first node 10 to a second node 12 multiplexed within a same fibre. At the second node 12 the optical signal whose wavelength is xcex1 is separated, dropped, and the remainder of the multiplexed signal is transmitted to the third node 13. Thus, this type of optical network has specific destinations serviced by signals at specific wavelengths. This simplifies the optical components tremendously because every signal characterized by a specific wavelength channel exits the network at a predetermined node. Unfortunately, this can also be disadvantageous because the network cannot be reconfigured conveniently. Reconfiguring the network is very beneficial because it allows the network to bypass equipment that is being serviced and it allows the network to boost the available bandwidth between specific nodes when there is a significant fluctuation in the bandwidth requirements between nodes.
Referring to FIG. 2, a configurable optical add/drop multiplexer, or COADM adds flexibility to the network. The COADM 20 has a wavelength dispersive element 21 for separating an optical signal at wavelength xcex1 from the received multiplexed optical signals. While it only diverts one signal, in this case at wavelength xcex1, it does attenuate all of the optical signals. The wavelength dispersive element 21 is optically coupled to a switch 22. The optical switch 22 can be set to either maintain the one signal within the network or optionally, the one signal is dropped from the network. If the one signal is dropped a new signal at wavelength xcex1, within the same wavelength channel as the one signal, is optionally provided. Recombining the optical signals requires a second wavelength dispersive element 23. Similarly, a second COADM 25 is added to control signals at wavelength xcex2. As shown in FIG. 2, the second COADM 25 has been set to keep the one signal at wavelength xcex2 within the multiplexed optical signal. Unlike a costly router, a COADM is not fast enough to switch individual packets of information, also known as internet protocol packets or IP packets; however, it is fast enough to allow the network to reconfigure itself based upon signal routing requirements. This solution is practical when the number of channels to be dropped is low, because each of the wavelength dispersing elements has a loss that all the optical signals experience. Generally, this approach is not recommend for serially add/dropping more than eight channels at each of more than eight nodes.
When larger numbers of wavelength channels must be added and dropped, an optical cross connect or OCX is used. Referring to FIG. 3, the OCX has two wavelength dispersive elements 31 and 32 in the form of arrayed waveguide gratings (AWGs). The first AWG 31 receives all the optical signals and separates them based upon their wavelength. Signals within each wavelength channel propagate down separate waveguides and into separate switches. The switch used to route each signal may drop it from the network or route it back into the network. The switch 33 is a 2xc3x972 switch, which gives it the ability to substitute an added signal at a same wavelength for an optical signal that is dropped. The OCX shown in FIG. 3 supports only four wavelength channels. The number of wavelength channels that an OCX can support is limited by the quality of the wavelength dispersive elements and the availability of the switches. Since optical signals propagate through the wavelength dispersive elements a maximum of two times the optical attenuation of the device is fairly low. Unfortunately, the OCX is very expensive. The two wavelength dispersive elements are expensive, the switches are expensive and handling the optical fibres during manufacture is time consuming and difficult. Additionally, the characteristics of the signals traveling through the OCX are very dependent on how well matched the two wavelength dispersive elements are one to another. Typically, the exact frequency response of one wavelength dispersive element is not precisely duplicated by any other. Using a tuning method, the frequency response of one such element can be tuned to another. This improves the matching of the two devices but unfortunately it is expensive. Alternatively, devices from a large batch may be tested, evaluated and paired with similarly performing devices. These tests and the handling of the devices is time consuming and require very expensive testing equipment. Additionally, the optical properties of the wavelength dispersive elements are subject to modification due to environmental changes, such as temperature; maintaining same environmental conditions on both wavelength dispersive elements adds to the complexity required to package the device. Clearly, it would be beneficial to have an OCX that is inexpensive, small, and reliable while having good optical properties associated with near perfectly matched wavelength dispersive elements.
The invention discloses an optical wavelength division multiplexer/demultiplexer device comprising: an input port for coupling a first multiplexed optical signal supporting a first plurality of wavelength channels; a plurality of output ports, each for providing a channelized signal of said first plurality of wavelength channels; a first plurality of input ports, each for coupling a channelized wavelength signal of a second plurality of wavelength channels; a first output port for providing a second multiplexed optical signal corresponding to said second plurality of wavelength channels; a second plurality of input ports, each for coupling a channelized wavelength signal of a third plurality of wavelength channels; a second output port for coupling a second multiplexed optical signal containing said third plurality of wavelength channels; and, an echelle grating disposed for separating the first multiplexed optical signal received from the input port into signals within individual wavelength channels and for directing each into a corresponding output port of the plurality of output ports, for combining a second plurality of signals within corresponding wavelength channels received from the first plurality of input waveguides into a second multiplexed optical signal and for providing the second multiplexed optical signal to first output port, and for combining a third plurality of optical signals within corresponding wavelength channels received from the second plurality of input ports into a third multiplexed optical signal and for providing the third multiplexed optical signal to the second output port.
Additionally, the invention describes an optical wavelength division multiplexer/demultiplexer device comprising: a first input waveguide; a first input port for coupling a first multiplexed optical signal containing a first plurality of wavelength channels to the first input waveguide; a second input waveguide; a second input port for coupling a second multiplexed optical signal containing a second plurality of wavelength channels to the second input waveguide; a first plurality of output ports, each for providing a channelized signal of said first plurality of wavelength channels from the first input port; a second plurality of output ports, each for providing a channelized signal of said first plurality of wavelength channels from the second input port; a first plurality of input waveguides; a second plurality of input waveguides; a first plurality of input ports, each for coupling a channelized wavelength signal of a third plurality of wavelength channels to an input waveguide of the first plurality of input waveguides; a second plurality of input ports, each for coupling a channelized wavelength signal of a fourth plurality of wavelength channels to an input waveguide of the second plurality of input waveguides; a first output waveguide for receiving a third multiplexed optical signal including said third plurality of wavelength channels; a first output port for coupling the third multiplexed optical signal from the first output waveguide; a second output waveguide for receiving a fourth multiplexed optical signal including said forth plurality of wavelength channels; a second output port for providing the fourth multiplexed optical signal from the second output waveguide; and, an echelle grating disposed for separating the first multiplexed optical signal received from the first input waveguide into signals within individual wavelength channels and for directing each to a corresponding output port from the first plurality of output ports, for separating the second multiplexed optical signal received from the second input waveguide into signals within individual wavelength channels and for directing each to a corresponding output port from the second plurality of output ports, for combining a plurality of signals within corresponding wavelength channels received from the first plurality of input waveguides into a third multiplexed optical signal and for providing the third multiplexed optical signal to the first output port, and for combining a plurality of signals within corresponding wavelength channels received from the second plurality of input waveguides into a fourth multiplexed optical signal and for providing the fourth multiplexed optical signal to the second output port.